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In a use-case diagram, use cases (bubbles) provide a functionality to an actor. For example, ecommerce site, actor "shopper" could use bubble "browse catalog" or "make payment".

In this case, should a bank in an ecommerce example like above be considered an actor? I think not, since the bubble "make payment" does not provide any functionality for bank. On the other hand, bank is involved in "make payment" as CC information is validated by bank.

Please help me understand. I have already seen posts like Actor in Use Case diagram
but it is not clear to me. Note I am not talking about use cases that have primary and secondary actors, I am talking about use case diagrams only.

PS. There is a main difference between my case and the post link above. The question there is about ATM, so naturally it would work with a bank actor. But in my case, E-commerce site only communicates with bank.

A similar example in my case would be an insurance company and hospital software. To register a patient, insurance must be verified with insurance company, but I am not sure if insurance would be an actor for my hospital softare.

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    You’re right that this question is a duplicate of the question you linked, therefore this question should be closed. If you don’t understand the accepted answer, you could ask for clarification there.
    – Rik D
    Oct 23, 2021 at 8:11
  • There is a main difference. The question there is about ATM, so naturally it would work with a bank actor. But in my case, E-commerece site only communicates with bank
    – Afia R. S.
    Oct 23, 2021 at 8:31
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    The bank in your scenario is like Swift in the other scenario.
    – Rik D
    Oct 23, 2021 at 13:48

1 Answer 1

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The use-case is not about functionality offered to actors, but about actor’s goals a system helps to achieve:

A use case is all the ways of using a system to achieve a particular goal for a particular user. Taken together the set of all the use cases gives you all of the useful ways to use the system, and illustrates the value that it will provide.
- Ivar Jacobson, inventor of use-cases, in "Use-Case 2.0"

The bank in your case is an actor: even if the bank does not directly use the functionality of your system, the bank is involved in the user's goal. Moreover, enabling their users to pay with their account also belongs to the goals of the bank. The bank is said to be a secondary actor.

Edit: More information on actors (optional reading)

The UML specifications are relatively agnostic about actors. It just explains that they are external to the system and correspond roles that users or other independent systems have in a use-case.

The use-case community has however a more precise understanding:

The primary actors are the ones for whom the system is built; they are the ones to whom the system provides sufficient economic value to warrant its construction.
- Kurt Bittner & Ian Spence in "Use case Modeling", 2002

The secondary actors are also called supporting actors:

A supporting actor in a use case is an external actor that provides services to the system under design. (...) We used to call this a secondary actor, but (...) More people are now using supporting actor, which is the more natural term.
- Alistair Cockburn in Writing effective use-cases, 2001

The convention is to place secondary actors on the right of the diagram if possible. More in Oracle's white paper "Getting Started With Use Case Modeling" (page 10), 2007

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  • Thanks. I did not know we could have secondary actors in use case diagrams. I had heard of secondary actors only for use cases. Could you kindly provide a book/article that discusses this?
    – Afia R. S.
    Oct 24, 2021 at 3:29
  • @AfiaR.S. Secondary actors are also called "supporting actors". It's not part of the UML specification but you'll find this notion (briefly) described in most of the reference books of use case litterature e.g. "Writing effectice use cases" (Cockburn), "Use case modeling" (Spence & Bittner), "More About Software Requirements: Thorny Issues and Practical Advice" (Wieger), but my favourite is "Use Case 2.0" (Jacobson, Spence, Bittner) and it's free (page 48).
    – Christophe
    Oct 24, 2021 at 11:27
  • @AfiaR.S. The notion is sufficiently known that there is a non-written convention to try to put the primary actors on the left and the secondary on the right of the use-case diagram. I'll try to gather some references and edit the post tomorrow evening (I'm currently faraway from my bookshelf).
    – Christophe
    Oct 24, 2021 at 11:30

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